Mechanical performance and consumer product safety have been major drivers for glass research and innovation. Strengthened glass products are omnipresent in daily life, from rooftop windows and automotive windshields to solar modules, partition walls and covers for handheld electronic devices. These applications rely on two strengthening technologies available today: chemical strengthening and thermal strengthening. The former involves immersing a glass product in a bath of liquid salt, at elevated temperature and for prolonged ion exchange time. While applicable to thin-walled glass products, it requires specialty glass formulations and high processing cost. As the alternative, thermal strengthening is straightforward, in principle, requiring nothing but rapid cooling of a glass product’s surface from above its softening temperature. However, the process of thermal strengthening as today’s most widespread method for enhancing the strength and reliability of glasses has reached maturity, leaving fundamental restrictions in terms of applicable glass thickness and type unresolved. In particular, these limitations involve the available wall thickness in relation to the ability to establish a thermal gradient upon cooling, and the available coefficient of thermal expansion governing the magnitude of the achievable strengthening effect. These limitations do not only prevent the further development of sustainable and efficient lightweight glass structures, but also exclude the process from the most prolific specialty glass applications. With the proof-of-concept project enjulii, we targeted a novel post-processing method for thin-walled glass products which overcomes the limitations of thermal strengthening by achieving a tenfold decrease in accessible glass thickness and/or coefficient of thermal expansion. The process relies on replacing conventional cooling in a stream of air by rapid immersion in a liquid, low-melting metal. This allows for significantly enhanced heat extraction rates, and makes thin-walled or low-expansion thermally strengthened glass products reality. The project broke ground for applying an otherwise intriguingly efficient technology to thin-walled glass products and glass compositions which were previously outside of the process’s capabilities. By this, novel applications and products become in sight, in particular, thermally strengthened glass fiber for light-guiding, illumination and light delivery applications, light-guiding rods glass rods with improved bending resistance and mechanical reliability, and strengthened glass capillaries for gas storage and handling. Enjulii set the stage for innovating these products towards commercial viability.
